This invention relates to a ball valve for the passage of fluids wherein the valve includes an integral bracket providing protection against blowout of the stem when subjected to high pressure and high temperature conditions, and more particularly to a ball valve with an integral bracket and a contiguous blowout prevention bushing.
Conventional ball valves are often subjected to extremely high pressures and temperatures in the various processes where they are used. Many prior art valves suffer in that they leak past seals associated with the rotatable closure members. The tendency for valves to leak increases under conditions of high pressure and high temperature, and is especially common in severe service valves which operate through a wide range of temperatures.
Ball valves operating under high pressure conditions often include a bonnet attached to the body of the valve to prevent blowout of the stem. The bonnet can be integral to the valve body, such as is disclosed in U.S. Pat. No. 6,095,493 to Velan, or can be separately bolted onto the valve body. However, the prior art bonnet designs suffer from shortcomings in their design.
The integral and bolt-on bonnet designs are similar in that they both cooperate with the stem to prevent blowout under high pressure conditions. One shortcoming of the prior art integral bonnet design is the required use of the split bushing and split glands that are necessary for the installation of the stem. The split gland and split bushing increase the number of critical parts for possible failure and increase the time necessary to install the stem as efforts must be made to ensure proper alignment of the stem within the stem passage. Misalignment of the stem in the stem passage of the bonnet can result in improper bearing of the axial load leading to leakage of the stem seals and unseating of the ball with the upstream and downstream seats. Furthermore, use of the split gland can result in an unbalanced compression of the packing rings, also leading to leakage in the valve.
The use of split-bushings requires the use of an additional bearing surface because the split bushing does not provide an adequate planar surface against which parts can freely move, instead requiring a thrust bearing located below the split bushing, and a stem bushing located above the split bushing. In addition, the prior art split bushing integral bonnet design features a long stem that extends above the bonnet. This creates a risk that axial movement of the handle can be translated through the stem to the ball, unseating the ball from the upstream and downstream inserts, and possibly damaging the seats.
Examples of valves featuring stems secured by plates and flanges are disclosed in U.S. Pat. Nos. 3,508,738, 4,342,444, 4,460,157 and 5,377,955.
In U.S. Pat. No. 3,913,610, Paptzun discloses a valve wherein the valve stem is contained within an integral housing. The housing is capped by a disc through which a threaded end of the stem extends. The opening through which the threaded end extends is smaller in diameter than the outer diameter of the stem, thereby providing a shoulder which secures the stem inside the integral flange housing.
In U.S. Pat. No. 4,475,712, DeJager discloses a valve designed to operate under high pressure conditions having an integral bonnet, wherein the valve stem is retained within the valve body. The valve stem has a shoulder with an outer diameter greater than the diameter of the stem passage. To install the stem in the DeJager valve, the body is equipped with an opening on the bottom through which the stem is inserted. The bottom opening is secured by a cover assembly which is secured into the valve body once the stem is inserted in the valve body.
Other patents of interest in the art include U.S. Pat. Nos. 4,479,513, 4,558,874, and 4,762,301.